1. Field of the Invention
The present device relates generally to an infrared imaging system. More specifically, the device relates to wide field of view, infrared imaging systems with mid-wave infrared bands and, optionally long-wave infrared bands.
2. Background
Infrared electromagnetic radiation refers to the region of the electromagnetic spectrum between wavelengths of approximately 0.7 and 1000 μm, which is between the upper limit of the visible radiation region and the lower limit of the microwave region. Infrared radiation is sometimes broken into three sub-regions: near-infrared radiation with wavelengths between 0.7-1.5 μm, intermediate-infrared radiation with wavelengths between 1.5-20 μm, and far-infrared radiation with wavelengths between 20-1000 μm. The intermediate-infrared radiation region is often further broken into the mid-wave (MWIR) region with wavelength limits of 3-5 μm and the long-wave (LWIR) region with wavelength limits of 8-12 μm.
Infrared radiation is produced principally by electromagnetic emissions from solid materials as a result of thermal excitation. The detection of the presence, distribution, and direction of infrared radiation requires techniques which are unique to this spectral region. The wavelengths of infrared radiation are such that optical methods may be used to collect, filter, and direct the infrared radiation. Photosensitive devices convert heat, or infrared electromagnetic radiation, into electrical energy and are often used as infrared sensitive elements. Such photosensitive devices respond in proportion to the number of infrared photons within a certain range of wavelengths to provide electrical energy.
Generally, an imaging infrared sensor includes a plurality of infrared sensitive elements in order to provide suitable resolution of the field of view which is to be monitored. In addition to the plurality of infrared sensitive elements, an infrared sensor includes other components for complete processing of the information provided by incident infrared electromagnetic radiation. Optical filters and apertures are used to define and focus the radiation directed at the infrared sensitive elements. Electronics are necessary for controlling the data collection and processing the collected data from the infrared sensitive elements. Cooling apparatus is necessary to maintain the operation of the infrared sensitive elements as well as the electronics. One approach for processing the electrical energy provided by the plurality of infrared sensitive elements is to use multiplexers to provide a single signal having a serial data stream since it is simpler to process the single resulting serial signal than the plurality of signals which correspond to the plurality of infrared sensitive elements. The serial signal is generally further processed by any number of techniques known in the art to provide interpretable, useful information regarding objects in the field of view of the infrared sensor.
As is known in the art, military and space applications employ infrared electromagnetic radiation detection for such functions as tracking and searching. These applications require the detection of low-level radiation in the intermediate infrared radiation range. One example of an application for infrared detection is in radar systems, where greater angular resolution and obstacle penetration capabilities improve overall platform imaging capabilities while the inclusion of infrared detection, particularly the detection of more than one band, or range, of infrared radiation, makes the system more difficult to jam, or disable.
Electro-optical sensor assemblies, such as infrared imaging systems, use optical components to route and focus received radiation onto a detector. However, the size and weight of electro-optical sensor assemblies have always been a significant design consideration. For example, in an airborne application, the size of the sensor assembly dictates the size of the required gimbal, which in turn affects the overall system size and weight. Since the sensor assembly and gimbal may both be in the airstream, the size of each can affect the overall aircraft drag. In another example, such as in ground applications, a head mirror may be used for elevation pointing. The number of optical apertures and the size of these apertures dictate the head mirror size, which, in turn, affects the size and weight of the surrounding armor plate.